Various time-temperature integrators have been proposed heretofore, for example, the integrator shown in U.S. Pat. No. 2,320,810 to Stoddard et al and in Myers U.S. Pat. No. 2,320,811, and the devices shown in Perry U.S. Pat. No. 3,392,584, Lever et al U.S. Pat. No. 3,186,228, and Cotton U.S. Pat No. 2,758,474. In general, such prior devices are relatively bulky relatively complicated and not adapted to be worn conveniently on the human body for the purpose of registering a person's expenditure of calories over a selected time interval.